1. Field of the Invention
The present invention relates to a zoom lens mechanism suitable for use with a zoom lens system such as that proposed by the assignee of the present application in U.S. patent application No. 09/534,307 (Japanese Patent Application No. Hei 11-79572).
2. Description of the Related Art
In a zoom lens system of the prior art, there are contradictory demands for a high zoom ratio and miniaturization. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, zoom paths) are determined (i.e., solutions for zoom paths) so that the zoom ratio becomes high, interference of the lens groups occurs on the telephoto side, or interference of a lens group and the image plane occurs on the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the zoom lens system cannot be obtained due to the mechanical structure thereof.
The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. Patent Application No. 09/534,307). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths.
Accordingly, it is an object of the present invention to provide a lens mechanism (lens barrel) suitable for use with a zoom lens system that includes the switching lens group as described above.
In order to achieve the above object, a zoom lens mechanism is provided for moving a switching lens group of a zoom lens system, the switching lens group constituting one of a plurality of variable lens groups of the zoom lens system which move in an optical axis direction upon zooming, and including first and second sub-lens groups, which are arranged in that order from the object side, wherein the first and the second sub-lens groups serve as a focusing lens group in a mutually close position and in a mutually distant position in the optical axis direction. The zoom lens mechanism includes a switching lens group frame supporting a first sub-lens group frame and a second sub-lens group frame in a manner that allows relative rotation and linear displacement of the first and second sub-lens group frames in the optical axis direction, the first and second sub-lens group frames supporting the first and second sub-lens groups, respectively; a shift cam mechanism provided on opposed surfaces of the first sub-lens group frame and the second sub-lens group frame, respectively, the shift cam mechanism causing the first and second sub-lens group frames to move to one of the mutually close position and the mutually distant position, in accordance with relative rotation between the first sub-lens group frame and the second sub-lens group frame; an actuator ring for providing the relative rotation between the first sub-lens group frame and the second sub-lens group frame, the actuator ring being rotatably retained in the switching lens group frame and engaged with the second sub-lens group frame to cause the relative rotation between the first sub-lens group frame and the second sub-lens group frame; a receiving surface provided on the switching lens group frame wherein a rear end surface of the actuator ring abuts against the receiving surface; and a biasing device for biasing the first sub-lens group frame toward the actuator ring to force the first sub-lens group frame, the second sub-lens group frame, and the actuator ring against the receiving surface, so that the shift cam mechanism provided on the first and second sub-lens group frames come into contact with each other.
Preferably, the shift cam mechanism includes a shift cam surface provided on the rear end of the first sub-lens group frame, and a follower projection, provided on the second sub-lens group frame, which projects in a forward direction and engages with the shift cam surface.
Preferably, the switching lens group frame includes a shutter retaining ring for retaining a shutter and a front annular member attached at the front of the shutter retaining ring. The first sub-lens group frame, the second sub-lens group frame, and the actuator ring are held between the shutter retaining ring and the front annular member. The biasing device is arranged between the front annular member and the first sub-lens group frame.
Preferably, a linear guide rod is provided in the front annular member in order to linearly guide the first sub-lens group frame in the optical axis direction. The biasing device includes a coil spring provided around the linear guide rod.
Preferably, the receiving surface is provided on the shutter retaining ring.
Preferably, a focus cam mechanism is provided on opposed surfaces of the actuator ring and the second sub-lens group frame, the focus cam mechanism moving the first sub-lens group frame integrally with the second sub-lens group frame in the optical axis direction, in accordance with the rotation of the actuator ring, while maintaining the first and second sub-lens group frames in one of the mutually close position and the mutually distant position.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-288547 (filed on Sep. 22, 2000) which is expressly incorporated herein in its entirety.